Preparation of alkyl metaborates



Oct. 10, 1967 T K ET AL 3,346,614

PREPARATION O F I XLKYL METABORATES 7 Filed Jan. 27, 1965 EBORIC ACID AIR N-ALKANE /|8 /|4 22 WATER, ETC. 1' V U CATALYST lo 20 OXIDATION- REACTOR 36 PROPANE :26 /22 RECYCLE 34 (28 TREATING SEPARATOR 2 STRIPPER (ALKANE) /58 WATER '44 /4o v 42 BORIC ACID E 48 S L' RECOVERY ESTER 54 ALCOHOL TREATMENT I 7 PRODUCT INVENTORS.

CHARLES M. STARKS EUGENE FLYNT KENNEDY ATTORNEY United States Patent 3,346,614 PREPARATION OF ALKYL METABORATES Charles M. Starks and Eugene Flynt Kennedy, Ponca City, Okla., assignors to Continental Oil Company, Ponca City, Okla., a corporation of Delaware Filed Jan. 27, 1965, Ser. No. 428,517 Claims. (Cl. 260-462) This invention relates to alkyl metaborates and particularly to the preparation of alkyl metaborates by oxidation of alkanes in the presence of boric acid or boron oxide. Still more particularly the invention relates to the recovery of alkyl metaborates from admixture with unoxidized alkanes.

Efforts have been made to prepare alcohol by oxidation of alkanes using the ability of boric acid to form borates which permit a greater per pass conversion of the alkane. The alkyl borate can be hydrolyzed to obtain the secondary alcohol. The borate can also be thermally decomposed to obtain olefins.

One of the major difliculties of this particular road lies in the tendency of the oxidation reaction to produce side reaction products, such as ketones, carboxylic acids and carboxylic acid esters. These side reaction products tend to become the major products as the conversion of alkane is increased.

One reason for pushing up the degree of conversion the alkane is to decrease the amount of unreacted alkane which needs to be separated from the product borates. However, even with conversions on the order of 50%, a very large amount of unoxidized alkane must be separated. It has been observed that under certain conditions of operation, the borate product is very heat sensitive and readily decomposes at temperatures needed for the removal of the unoxidized alkane.

An object of the invention is a process for preparing alkyl meta-borates. A particular object of the invention is a process for oxidizing alkanes in the presence of boric acid, or boron oxide to produce metaborates predominating in groups having only one hydroxyl constituent.

Another object of the invention is a process for re: covering metaborates from admixture with alkanes. A preferred object of the invention is a combination process for free Oxygen oxidation of certain alkanes in the presence of boric acid or boron oxide to produce a product consisting essentially of alkyl metaborates, recovering these m-etaborates from unoxidized alkane, and recovering the corresponding secondary alcohol from the metaborate.

Other objects of the invention will become apparent in the course of the detailed description thereof.

The sole figure shows a schematic drawing of a combination process for producing secondary alkanols from n-alkanes by the process of this invention.

One process of the invention comprises reacting liquid alkane having 620 carbon atoms with free oxygen at a temperature of between about 160 C. and 200 C. to convert not more than about 20% of said alkane to a reaction product mixture consisting essentially of alcohols; said oxidation being carried out in the presence of a boron compound selected from the class consisting of boric acid and boron oxide, in an amount of at least about 1 mole of boron per mole of alkane converted whereby alkyl metaborate is obtained; and continuously removing from said reaction zone water produced therein.

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The oxidation of liquid alkanes in the presence of boric acid or boron oxide results in the production of compounds including hydroxyl, carbonyl, carboxylic and carboxylic ester groups. The preferred product is a secondary alkanol. It has been discovered that a product metaborate mixture which produces secondary alkanols as the predominant reaction product component are produced by controlling the operating conditions, the degree of conversion and the amount of boron present. In the oxidation process of the invention alkane having 620 carbon atoms is reacted with free oxygen. The alkane is in the liquid state.

The process may be applied to a single alkane or to a mixture of alkanes. The alkane feed is desirably an nalkane as the secondary alkanol produced make desirable intermediates for the production of ethoxy alkanol surfactants. The n-alkanes having 10-20 carbon atoms are a preferred feed. Illustrative alkanes are hexane, octane, nonane, n-dodecane, n-tetradecane, n-hexadecane, noctadecane and eiscosane.

Sufiicient pressure is maintained in the oxidation reaction zone to keep the alkane essentially in the liquid state, but also to permit water produced in the reaction zone to be continuously removed therefrom.

The oxidation is carried out using free oxygen, air or a synthetic mixture of oxygen and an inert gas. Generally, a small excess of oxygen is introduced and the oxygen uptake is controlled by maintaining some free oxygen in the gas withdrawn fromthe oxidation zone.

The oxidation zone is maintained at a temperature between about C. and about 200 C.; desirably the upper temperature is maintained below about 180 C.

It has been found that when not more than about 20% of the alkane feed is converted to compounds including combined oxygen, that the reaction product mixture recoverable from the metaborate product consists essentially of alcohols in the sense that essentially all of the compounds incl-ude one hydroxyl group. A minor amount of compounds also include another oxygen group. For re action product mixture, wherein essentially all of the compounds include a hydroxyl group, the conversion of alkane is held between about 10% and 15%.

The oxidation is carried out in the presence of boric acid or boron oxide. The boric acid may be charged either as the orthoboric acid or the nietaboric acid. The acid may be charged as an aqueous solution since the water will be removed along with the water formed.

It has been observed that the desired metaborate prod not and predominantly the alkyl metaborate product is obtained when the boric acid or boron oxide is present in an amount of at least about one mole of boron per mole of alkane converted. Somewhat less than this amount may be charged successfully since even under the optimum conditions some product is obtained which will not react with the boron. In any case, suificient boron should be available to produce the metaborate product as essentially the only borate product.

For purposes of definition, the structural configuration of alkyl metaborate is shown as Formula I.

The oxidation reaction is capable of proceeding in the absence of a catalyst. It is pointed out that many alkanes obtained from petroleum include compounds which are inhibitors for the oxidation reaction. Normally these inhibitors can be removed by a concentrated sulfuric acid wash operation. The oxidation reaction time is decreased by having present in the oxidation zone a catalyst for the alkane oxidation. Essentially any metal which is capable of existing in more than one valence state is more or less effective as a catalyst for this reaction. It is preferred to use as the oxidation catalyst a compound of cobalt, nickel, iron or manganese. The compounds may be a completely inorganic salt or a fatty acid salt, i.e., cobalt nitrate, cobalt acetate and cobalt stearate. The amount of catalyst compound added is dependent upon the type of metal and the type of alkane charged.

The metaborates, whether alkyl metaborates or metaborates where the organic radical includes combined oxygen other than hydroxy oxygen, are extremely heat sensitive. Under ordinary distillation conditions for the removal of unoxidized alkane, it is dilficult to avoid substantial heat decomposition resulting in the formation of olefins. It has been found that a solution of metaborate and unoxidized alkane from the oxidation zone can be separated to obtain metaborate essentially free of alkane by a stripping operation. The solution is atomized into a chamber at a temperature below the decomposition temperature of the metaborate content. Generally, the atomizing temperature is not more than about 250 C. and preferably is not more than about 200 C.

The atomized solution is contacted in the chamber with a stripping agent which vaporizes the alkane content of the atomized solution, which passes out of the chamber along with the stripping agent. The stripping agent is introduced into the chamber at about the same temperature as that of the atomized solution. Metaborate product essentially free of alkane is removed from the stripping chamber.

The stripping agent may be any gaseous or vaporous material which is inert to the alkane or the metaborate. Where the contacting time is short, air may be used as a stripping agent. The preferred stripping agent is alkane having 1-4 carbon atoms, and particularly, propane or isob-utane. These have the advantage of being readily separable from the alkane feed. Natural gas may be used as a stripping agent. If desired, the stripping chamber may be operated at a vacuum.

It is to be understood that the stripping invention is not limited to a solution of any particular metaborate content. As a practical matter the oxidation conversion is limited to a maximum of about 50%. The stripping chamber permits the control of temperature plus an extremely rapid removal of alkane such that large volumes of alkane can be economically handled. Therefore, the stripping chamber invention is applicable to any solution ranging from the lowest conversions to the highest practical conversions.

The combination process of the invention is described in connection with the figure. In the figure the oxidation reaction zone is depicted as a box 10. n-Alkane feed,

herein n-tetradecane is passed by way of line 12 into reactor 10. Oxygen for the oxidation is supplied by air which is introduced by way of line 14. Oxidation catalyst is introduced by way of line 16; herein the catalyst is cobalt nitrate. With a cobalt catalyst the usage falls in the range of 0.001 to 0.01 mole percent, based on alkane feed. Boric acid and recycle boric acid in the form of an aqueous solution are introduced into reactor 10 by way of line 18. Theoretically, one mole of meta borate acid is required for each mole equivalent of alcohol produced. Under the moderate conversion condition for this process about one mole of boron is required for each mole of alkane oxidized, i.e., converted. For conversions in the range of 1020%, the boric acid (H 80 requirement is in the range of about 57 weight percent. 7

Herein reactor 10 is operated at a temperature of 175 C. at an atmospheric pressure. Conversion is held to which is reached in a time of about 2.5 hours. Air is introduced at about 50 volumes at STP per volume of hydrocarbon. The effluent gas stream which passes out of reactor 10 by way of line contains water of reaction and from the boric acid stream, small amounts of carbon monoxide, carbon dioxide and gaseous hydrocarbons. The nitrogen-oxygen component is approximately 10% oxygen. The reactor is operated to maintain a constant amount of unreacted oxygen in efiluent stream 20.

Under these conditions, it has been observed that essentially all of the product compounds contain a hydroxyl group. The reaction product compounds include carbonyl groups, carboxylic groups and carboxylic ester groups. It appears that these groups are in the main a second group attached to an alkanol.

A solution of metaborates, essentially alkyl metaborates, dissolves in the unoxidized tetradecane is withdrawn from reactor 10 and passed by way of line 22 into stripper 24. By means not shown, the solution in line 22 is heated to a temperature of 200 C. and enters stripper 24 as a fine spray after passage through an atomizer nozzle not shown. Herein propane is used as the stripping gas and is passed into stripper 24 by way of line 26 at a temperature of 200 C. A vapor stream of propane and tetradecane passes out of stripper 24 by way of line 28 into separator 30' where the propane is separated from the tetradecane and recycled by way of lines 32 and 26. The recovered tetradecane is passed from separator 30 by way of line 34 into alkane recycle treating zone 36.

' Under some conditions there may be no treatment of the recycle alkane. However, it is preferred to remove 'the carboxylic acids dissolved in the alkane. This can be done by caustic washing of the stream. The stream also contains some ketones and the yield of ultimate alcohol can be increased by a hydrogen treatment of the stream to convert ketones to the corresponding alcohol.

An alkyl metaborate stream which is on the order of 90% sec-tetradecanol providing the alkyl portion, and is essentially free of alkane, i.e, on the order of 1% of tetradecane, is passed by way of line 40 into the hydrolysis reactor 42. The hydrolysis is a conventional procedure wherein about 2 volumes of water fromline 44, per volume of metaborate, are agitated in reactor 42, at a temperature of 90100 C. In general, the hydrolysis time is on the order of 0.5-1 hour.

The boric acid water layer is withdrawn from reactor 42. The crude alcohol remaining is Washed with hot water until all of the boric acid has been removed. The washings and the aqueous boric acid are passed by way of line 48 to boric acid recovery operation 50. The crude alcohol stream is passed by way of line 52 to alcohol treatment (purification) zone 54.

The hot aqueous boric acid may be concentrated for 0 recycle by way of lines 58 and 18 to oxidation reactor reactor 10, without upsetting the oxidation-borate formation operation.

The crude alcohol stream from hydrolysis reactor 42 may be hydrogenated to remove the color bodies and then distilled into a secondary alcohol concentrate.

For surfactant use it has been observed that the crude alcohol stream must 'be distilled to remove some high boilers, and then may be sent to surfactant production operation. In a typical situation alcohol product stream line 60 is reacted with ethylene oxide to form an ethoxylated stream which can then be sulfated'to produce an ethoxy sulfonate detergent. Preferably, the ethoxylate reaction is carried out using BF catalyst. The ethoxylate is normally alight yellow in color and can be made colorless by hydrogenation using a nickel catalyst.

The above has set out a combination operation for producing a product which is essentially secondary tetradecanol. It is to be understood that any of the alkanes hereinbefore described may be charged to such a combination process at any set of conditions in the ranges described hereinbefore.

Illustrations A mixture of n-alkanes from urea adduction of kerosene was used as feed. The mixture had the following composition:

Alkane Weight percent n-undecane 0.9 n-dodecane 32.5 n-tridecane 33.4 n-tetradecane 32.3 n-pentadecane 0.9

in hydrocarbon) were maintained as constant as possible throughout all oxidation cycles.

The reaction mixture was stripped of unreacted alkane and other volatile materials by two passes through a 2- inch ASCO wiped-film distillation apparatus. The first pass was conducted at l160 C. at 2 mm. Hg and the second pass at 170-180 C. at 0.5 mm. Hg. The overhead products from both passes were combined with the Dry Ice trapped overhead from distillation and the organic material recovered from the traps of the oxidation apparatus. These combined distillates and trap materials were used as is in the charge for the next oxidation cycle. No attempt was made to account or compensate for the small amount of oxygenates in the recovered alkanes.

Other operating conditions for the 7 cycles are shown in Table 1.

TABLE 1 Weight Average Weight Percent Airflow Average Oxidation Percent Selec- Cycle Rate (1 O Uptake Time Alkane tivity to minute) (L/minute) (hours) Conver- Composite siou Oxidation Alcohol Cobalt nitrate was used as the oxidation catalyst in all cycles except No. 2 where cobalt acetate was used, which may account for the lower selectivity of cycle No. 2.

The residue from the stripping operation, consisting Inostlyof borate esters, was hydrolized by stirring at C. with 2 1. of water for one hour. The upper organic layer was separated and washed with two 1 1. portions of hot water. The crude brown oxidation alcohol was then distilled (B.P. 175 C. at 1 mm. Hg) without fractionation through a Claisenhead distillation apparatus. The distillate, termed composite oxidation alcohol, was invariably yellow and had a burnt-candle odor. In two experiments, the distillation was conducted in the presence of a base: cycle 4 over 50 g. of calcium hydroxide and cycle 6 over 15 g. of sodium hydroxide.

TABLE 2.-ANALYTICAL DATA FOR CRUDE OXIDATION ALGOHOLS Analytical Data Mole Percent Functional Group C cle y Percent 00 Sap. Acid 0 Number Number Number 0H 00 00 R CO H (p.p.m.)

Temperature C.), stirring rate (ca. 800 r.p.m.), and air inlet tube (4 mm. diameter, ca. 20 cm. depth Cycle 7 shows a large increase in functional groups other than OH when the conversion went to 26.0% as well as a decrease in selectivity.

TABLE 3.--ANALYTICAL DATA FOR "COMPOSITE, OXIDATION ALCOHOLS Analytical Data Mole Percent Functional Group C cle y Percent 00 Sap. Acid 0 Number Number Number OH 00 00 R COzH (p.p.m.)

1 Crude alcohol distilled over 50 g. of calcium hydroxide. 2 Crude alcohol distilled over 15 g. of sodium hydroxide.

'7 Cycles 4 and 6 show the favorable eiTect on acid content of the hydroxide treatment during distillation.

The buildup of oxygen compounds in the alkane recycle was followed. The amount of ketones, acids and esters was calculated on the assumption that the molecular weight of the alkane and that of the oxygen compounds were approximately equal.

TABLE 4.-OXYGENATED IMPURITIES IN RECYCLE ALKANE Data in Table 5 demonstrate the improvement to be gained in the recycle alkane by hydrogenation and caustic washing. The alcohol formed by the reduction of ketones will be recycled into the oxidation mixture where it will be recovered as additional borate ester.

of alkylmetaborate and alkane in a chamber where the atomized solution is contacted with a stripping agent, at about the same temperature as said solution, and recovering alkylmetaborate product essentially free of said alkane. 2. A process in accordance with claim 1 wherein said stripping agent is an alkane having 14 carbon atoms. 3. A process in accordance with claim 1 wherein said atomizing temperature is not more than about 200 C. 4. A process in accordance with claim 1 wherein said atomizing temperature is not more than about 250 C. 5. A process in accordance with claim 4 wherein said stripping agent is propane.

6. A process in accordance with claim 4 wherein said stripping agent is isobutane.

7. A process in accordance with claim 1 wherein said alkane is n-alkane having 10-20 carbon atoms.

8. A process in accordance with claim 7 wherein said alkane is n-tetradecane.

9. A process in accordance with claim 7 wherein said alkane is n-hexadecane.

Thus having described the invention, what is claimed is:

1. In the process where a liquid alkane having 6-20 carbon atoms is oxidized with free oxygen at a temperature between about 160 C. and about 200 C. to convert alkane to corresponding compounds having a hydroxyl group, in the presence of a boron compound selected from the class consisting of boric acid and boron oxide in an amount of at least one mole of boron per mole of alkane converted whereby a solution of alkylmetaborate and alkane is obtained, the improvement comprising: at a temperature below the decomposition temperature of the alkylmetaborate, atomizing the solution 10. A process in accordance with claim 7 wherein said alkane is n-dodecane.

References Cited UNITED STATES PATENTS 1,947,989 2/1934 Hellthaler 260-462 x 2,721,180 10/1955 Lawrence @161 25249.6 3,109,864 11/1963 Fox 6161 260-462X 3,243,449 3/1966 Winnick 260-462 CHARLES B. PARKER, Primary Examiner.

B. BILLIAN, Assistant Examiner. 

1. IN THE PROCESS WHERE A LIQUID ALKANE HAVING 6-20 CARBON ATOMS IS OXIDIZED WITH FREE OXYGEN AT A TEMPERATURE BETWEEN ABOUT 160*C. AND ABOUT 200*C. TO CONVERT ALKANE TO CORRESPONDING COMPOUNDS HAVING A HYDROXYL GROUP, IN THE PRESENCE OF A BORON COMPOUND SELECTED FROM THE CLASS CONSISTING OF BORIC ACID AND BORON OXIDE IN AN AMOUNT OF AT LEAST ONE NICKEL OF BORON PER MOLE OF ALKANE CONVERTED WHEREBY A SOLUTION OF ALKYLMETABORATE AND ALKANE IS OBTAINED, THE IMPROVEMENT COMPRISING: AT A TEMPERATURE BELOW THE DECOMPOSITION TEMPERATURE OF THE ALKYLMETABORATE, ATOMIZING THE SOLUTION OF ALKYLMETABORTE AND ALKANE IN A CHAMBER WHERE THE ATOMIZED SOLUTION IS CONTACTED WITH A STRIPPING AGENT, AT ABOUT THE SAME TEMPERATURE AS SAID SOLUTION, AND RECOVERING ALKYLMETHABORATE PRODUCT ESSENTIALLY FREE OF SAID ALKANE. 